Synergy is a Half-Life 2 co-opertive multiplayer modification. We have evolved from multiple mods (DC Co-op 2, Dev Co-op and Tim-Coop) to offer you the greatest co-op experience. This modification strives to give Half-Life players a true Half-Life 2 cooperative experience. The mod features our own levels and the ability to play the Half-Life 2, Episode One and Episode Two campaigns co-operatively. In addition, you can add more content by installing third-party mods, such as ROCK 24 and MINERVA: Metastasis, then playing them in Synergy!

Synergy was once the best Coop mod out there. Before it went to steamworks.

Before it went to steamworks it had awesome maps, badass new guns, custom player models, lots of other things, but then they went to steamworks and it unfortunately got bad. They ripped everything off it and left the custom player models just to donators.

The only thing I still like in this game is the "Trials" pack of maps. Only good thing left in it.